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Sept. 7, 2011 -- A chemical found in a wide range of consumer products may be harmful to children's mental and behavioral development and muscular coordination, a study shows.

The study is published in Environmental Health Perspectives.

Phthalates (pronounced thal-ates) are used to make plastics more flexible and durable. They are also used as solvents.

The chemicals are used in products that include car interiors, floor tiles, raincoats, nail polish and other cosmetics, synthetic leathers, and food packaging.

An increasing number of studies show evidence that phthalates may be harmful, particularly for young children.

It is not clear how they disrupt development. But some evidence suggests that the chemicals may affect thyroid hormone levels. These hormone levels play a key role in prenatal and newborn brain development, according to the study.

Phthalates may also reduce the amount of testosterone produced in the body, says study researcher Robin M. Whyatt, DrPH. Whyatt is deputy director of the Columbia Center for Children's Environmental Health at Columbia University.

Testosterone is important for male sexual development. It also plays a role in brain development for both boys and girls, Whyatt says.

"There are lots of potential ways that this is acting," she says. "We are at the beginning in our understanding of these mechanisms."

Evaluating Children's Development

The study is the first to look at the impact of phthalates on preschoolers. Whyatt and her team studied 319 children born between 1999 and 2006.

The researchers measured the level of each mother's exposure to four common phthalates during pregnancy by doing a single urine analysis of each mother-to-be. They also did regular urine analysis of 48 of the mothers for six to eight weeks in the latter stages of pregnancy.

Each child underwent an evaluation at age 3 that assessed mental, muscular coordination, and behavioral development.

The researchers report that two of the phthalates -- Mono-n-butyl phthalate (MnBP) and mono-isobutyl phthalate (MiBP) -- were significantly associated with delays in developing muscular coordination. Those delays increased with increasing concentrations of phthalates.

Among girls, MnBP was also associated with delays in mental development. Among boys, MnBP was linked to withdrawn behavior and an increase in mood changes, panic, whining, and worrying.

Another phthalate -- mono-benzyl phthalate (MBzP) -- was associated with anxious and depressed behavior. Among girls it was also linked with complaints of symptoms such as headaches and stomachaches.

"I was surprised and pretty depressed, particularly by the behavioral problems," Whyatt says of her reaction to the study results. "We didn't expect to see that at all, but it was a consistent pattern and highly significant. ... These are really consistent findings right down the line."

Findings Spark Controversy

"This study is further confirmation that prenatal exposure to phthalates is harmful to the development of our children's brains," the NRDC's Sarah Janssen, MD, says in a statement.

However, the American Chemistry Council (ACC), which represents the chemical industry, disputes the validity of the study.

"Since all of the children in the study appear to be within the normal range of variability, it appears the authors' conclusion -- that the minor differences seen in the study are indicative of behavioral problems -- is not supported by the science," reads the statement, which questioned the study's methods. "It is inappropriate to suggest that a spot measurement from the pregnant mother can be associated with behavioral effects in her child."

Whyatt was quick to respond:

"I have no idea what ACC would call 'normal' but it should be noted that 17.6% of children in our study evidenced risk of motor [muscular coordination] delay; 27.9% evidenced risk of mental delay and 12.9% were in the clinical range for internalizing behaviors," she writes in an email. "No matter how you characterize it, these proportions are concerning."

As for the "spot measurement," Whyatt stands by the method she and her colleagues used.

"We, in fact, did a lot of work to evaluate the reliability of the biomarkers used in this study," she writes. Whyatt is convinced that the impact of phthalates on a child's development is something to be taken very seriously; however, she says, there is little that can be done to avoid the chemicals, which are found everywhere.

"I wish I had some advice to offer," she says.

Whyatt does agree with the ACC that there are numerous factors that may put a child's development at risk and that phthalates are just one of them. However, she says, simply because multiple risk factors may be at play is not grounds for dismissing the risks posed by phthalates.

But there are also factors that play a positive role for growing children that Whyatt says have a far greater impact on their development.

"The most important thing is how parents interact with their children, that they read and play with them," she says. "Reading and playing are way more important than these risk factors."